A tongue and groove joint between adjacent planks boards or panels is well known, and at the present time the use of planks provided with tongues and grooves on opposed side edges thereof is common in the formation of floors for houses or other such buildings. In laying such a floor the tongue provided on one side edge of one plank is inserted into a corresponding groove provided on one side edge of an adjacent plank, and the tongue and groove are of substantially the same size so that when the tongue and the groove have been interconnected the two planks are substantially rigidly interconnected and also the joint between the planks is substantially draught-proof.
Tongue and groove joints are also utilised in many other applications, and are utilised in connection with planks made of wood, panels or boards made of chipboard or other such materials, and even with larger panels, such as panels formed of concrete or the like.
Planks boards and panels made of wood, chipboard or the like tend to expand when they are wet, or when used in a moist atmosphere. When planks boards or panels interconnected by means of tongue and groove joints are utilised in damp conditions, the planks or boards expand and, for example, in the case of floor, the planks may become distorted and may move from their original position so that the floor is no longer planar. Similar distortions occur in other structures formed from panels or boards having tongue and groove connections, particularly items such as garage doors. More particularly this has been found to be a particular problem in connection with garage doors or tongue and groove panels or the exterior of a house where, of course, the planks panels or boards are frequently subjected to conditions of high humidity.